1. Field of the Invention
The present invention relates to an apparatus and method for recording a digital signal, and more particularly to such an apparatus suitable for use in recording a digital signal transferred from a computer or the like.
2. Description of the Prior Art
Data stored in a hard disk or the like of a computer is, in practice transferred to and recorded by a data streamer (data-recorder) once a day so as to protect the data or back up the same.
For this operation or as a data recorder, analog audio tape recorders have been conventionally used in many cases. However, the analog tape recorders have disadvantages in that they need an excessive amount of a recording medium, e.g. magnetic tape, for recording and operate at a quite low data transferring rate upon recording, so that it takes a long time to transfer and record such data information. Moreover, the analog tape recorders have problems such as the starting point of a desired portion of the recorded data information cannot be rapidly searched for, and so on.
Thus, to overcome the above-mentioned problems, it is thought to utilize a helical-scan type DAT (digital audio tape recorder) using a rotary head, that is, a so-called DAT as a data recorder which has been recently comercialized. Such data recorders utilizing a DAT are described in U.S. patent application Ser. Nos. 133,010 filed Dec. 15, 1987, 177,624 filed Apr. 5, 1988, 210,229 filed Jun. 23, 1988 and 220,028 filed Jul. 15, 1988, by the same assignee of the present application.
To utilize the DAT as a data recorder, data transferred from a host computer is transformed in accordance with a DAT format before recording. In the DAT format, one frame is made up of two oblique tracks formed by one rotation of two heads respectively having a different azimuth angle with each other. 16-bit PCM audio data, which has been interleaved, and auxiliary sub-data are recorded in this one frame area as a unit. In this recording event, there are formed in each track a main area for recording the PCM data and a sub-area for recording the sub-data.
With the DAT as described above, when another signal is to be recorded on a previously recorded recording medium or tape, previously recorded signals are erased by recording new signals thereover, that is, by a so-called overwriting, without using an erasing head. Therefore, if overwriting is not normally effected, for example, due to clogging of the head or the like, there is the possibility that a part of the previously recorded signals will remain unerased. Therefore, if overwriting is not normally effected, for example, by the fact that a tape is momentarily loses contact with the heads or due to clogging, previously recorded signals may remain unerased, which causes a data error referred to as "drop-in".
To attend to this data error, in the DAT format, an error detecting code is added to each of the main areas and the sub-areas of each track in which signals are recorded, so as to detect an unerased portion, if any, in the track as an error.
When data from a computer is recorded in a data recorder, the signal processing will be facilitated if any period is known at every predetermined amount of the data.